1. Field of The Invention
This invention relates to methods for severing tube sheets to expose the bores of hollow fibers embedded therein.
2. Prior Art
In the making of one type of membrane gas separator the end of a bundle of hollow fiber membranes is placed in a cylindrical mold and a liquid casting resin is poured into the mold and cured. The configuration of the mold is such that the solidified casting can be used as a tube sheet in a cylindrical shell. It is then necessary to cut the tube sheet to expose bores of the hollow fibers so that a gas can pass through the tube sheet via the fiber bores.
Several methods have been proposed for cutting the tube sheet but none has been entirely satisfactory. The primary problem is that most methods used for cutting the tube sheet results in many of the hollow fibers being smeared such that the fiber bores are closed.
U.S. Pat. No. 3,503,288 discloses a method for cutting hollow plastic filaments embedded in a solid plastic matrix to expose the bores of the filaments wherein the end of the tube sheet is brought into contact with a cutter and is then rotated so that the cutter trims the end of the tube sheet. This patent states that attempts have been made to fracture the tube sheets by the use of a controlled bending force or a shaped explosive charge. The patent further states that, when an attempt is made to fracture a tube sheet larger than two inches in diameter, the resultant fracture is erratic, difficult to predict and usually damages beyond repair the integrity of the seal between the cast wall, the hollow filaments and the casing in which the tube sheet is mounted.
U.S. Pat. No. 4,183,283 discloses that a tube sheet can be severed in any suitable manner and then a thin layer of the tube sheet is removed by using a knife blade edge to scrape the severed face of the tube sheet and open the bores of hollow fibers embedded in the tube sheet.
U.S. Pat. No. 4,271,740 discloses apparatus for cutting a tube sheet having a fiber bundle embedded therein, the apparatus being provided with a pair of blades positioned at different angles.
U.S. Pat. No. 4,369,605 discloses the opening of bores in a cast tube sheet by severing the tube sheet and then grit-blasting the severed face of the tube sheet to open the fiber bores.